In an electronic device, for example, a projection type display device, provided with a discharge lamp (hereinafter referred to simply as lamp), it is desired that the light quantity of the lamp can be freely increased or decreased (dimmed) according to the ambient brightness. When the light quantity of the lamp is reduced, the power consumption of the lamp is reduced, and the temperature rise in the housing including the lamp is also prevented. Therefore, the power consumed by cooling means, such as a fan, is also expected to be reduced. Usually, the dimming of a lamp is performed in the range of about 80 to 100% of the rated power of the lamp. When the light quantity of the lamp is to be further reduced, it is only necessary that the power supplied to the lamp is reduced below the power corresponding to the normal dimming range of the lamp.
However, when the lamp is lighted with power less than the rated power or less than the power corresponding to the normal dimming range of the lamp (hereinafter referred to as low power operation), the temperature in the bulb (light emitting tube) cannot be maintained at a temperature at which a halogen cycle occurs. This results in a problem that blackening of the bulb is caused and thereby the light quantity of the lamp is reduced.
When tungsten (W), which is usually used as an electrode material of the lamp, is energized, the tungsten is made incandescent at a high temperature, so as to be evaporated. The evaporated tungsten is moved near the inner wall surface of the bulb, temperature of inner wall surface being comparatively low. Near the inner wall surface of the bulb, the evaporated tungsten is combined with halogen (X) in the bulb, so that tungsten halide (WX2) is formed. The vapor pressure of the tungsten halide is comparatively high, and hence the tungsten halide is circulated, in a gaseous state as is, in the bulb by convection. When the tungsten halide is heated in the vicinity of the electrode to a predetermined temperature (about 1400° C.) or higher, the tungsten halide is dissociated into halogen and tungsten. The tungsten resulting from the dissociation is returned to the electrode, and the halogen resulting from the dissociation repeats the same reactions as described above. A series of these chemical reactions is referred to as a halogen cycle. The blackening of the bulb means a state where black powder derived from the evaporated tungsten is stuck to the inner wall surface of the bulb.
In order to prevent the blackening due to the low power operation of the lamp, a lamp refresh process, in which power necessary for generating the halogen cycle is supplied to the lamp only during a predetermined time period at predetermined time intervals set beforehand by a lamp manufacturer, or the like, needs to be performed according to the operation power of the lamp. A method of refreshing a lamp is also described, for example, in Japanese Patent Laid-Open No. 2009-93862 (Patent Literature 1).
However, even in an electronic device which includes a lamp and which is configured to execute the lamp refresh process, there is a case where, when, after shipment of the electronic device, the low power operation of the electronic device is performed by a user, or the like, the blackening is caused in the lamp even though the lamp has not reached the end of its lifetime cycle. In this case, it is not easy to identify the cause of the blackening.
The lamp is used in the electronic device which includes a lamp power supply for stably supplying power to the lamp, and a control section for controlling the refresh operation of the lamp, and the like. Further, an operable temperature range is usually specified for the lamp. For this reason, when the blackening is caused in the lamp operated at a low power level, various causes, such as a failure of the lamp itself, a failure of the lamp power supply section, a control failure of the lamp refresh process, an unsuitable temperature control of the lamp, and an unsuitable installation environment of the electronic device, are considered as causes of the occurrence of blackening.